One of the main causes for repeated addict relapse is thought to be the direct conditioning of morphine responses in the central nervous system. The role of morphine as a hedonic agent will be investigated by comparing single unit responses in various subcortical loci to the effects of other less pathological rewards (food and intracranial self-stimulation). One goal will be to determine if morphine uses the same reward sites as these other agents and the correlation between them. In addition to these direct tests to compare a natural reward, brain stimulation and morphine, tests will be made to condition the morphine-induced neuronal responses to previously neutral stimuli to determine if and where responses can be conditioned. The basis for this is the hypothesis that morphine causes a relatively long-lasting hedonic response under some conditions which may be manifest within this system. Electrodes will be placed in known food reward sites (medial and lateral hypothalamus), sites which support ICSS (locus coeruleus, hypothalamus and other catecholamine centers), medial thalamus and other sites previously implicated to be involved in various aspects of morphine's action. The significance of this study should lie in a better understanding of the mechanisms involved in craving and how morphine "borrows" these systems from natural rewards. It will also provide a picture of what parts of the brain's response to morphine are amenable to conditioning and how these may be applied to behavioral therapy for post-addicts.